1. Field of the Invention
The present invention relates to a headrest, and, more particularly, to a movable headrest which is provided on the seat back of a seat of a vehicle and changes its position from a normal position to an emergency position at the time of occurrence of a rear-end collision, thereby preventing the neck or so of a passenger from being damaged.
2. Description of the Related Art
A headrest is provided on an upper portion of the seat back of a seat of a vehicle to receive the head of a passenger including a driver when the vehicle is hit from behind, preventing a so-called whiplash injury. Recently, various kinds of movable headrests (also referred to as “active headrests”) with an enhanced performance for protecting the head, neck etc. have been proposed. At the time of a rear-end collision, this movable headrest instantaneously changes the position of the headrest body which receives the head of a passenger frontward, thereby protecting the head, the neck or the like of the passenger.
The movable headrest generally includes a position changing mechanism which changes the position of the headrest body in a normal use position (hereinafter referred to as “normal position”) to a desired position (hereinafter referred to as “emergency position”) when a rear-end collision occurs. The movable headrest further includes a position hold mechanism which holds the headrest body, shifted to an emergency position, in the emergency position. The position hold mechanism prevents the headrest body, shifted to the emergency position by the impact of the collision, from reversely returning to the normal position, so that the headrest body can keep receiving the head of the passenger. Further, the movable headrest includes a position return mechanism which releases the holding of the position of the headrest body held by the position hold mechanism as needed. The position return mechanism permits the headrest body moved to the emergency position to return to the normal position. Movable headrests of this kind are disclosed in, for example, Japanese Unexamined Patent Publication No. 2002-142910 (Patent Document 1), Japanese Unexamined Patent Publication No. 2006-264431 (Patent Document 2), and Japanese PCT National Publication No. 2006-511398 (Patent Document 3).
The position changing mechanism of each of the movable headrests disclosed in Patent Document 1 and Patent Document 2 employs a link structure which has a plurality of arm-like link members coupled together. In the position changing mechanism, impact force generated when a head of the passenger hits against the headrest is directly applied to the individual link members. When impact force is applied to the headrest body from above or side, the individual link members receive the impact force, which may cause the problem of deformation or damage of the link members. When the link members are thus deformed or damaged, malfunction occurs in the operation of the position changing mechanism, so that the headrest body may not return to the original normal position.
The position hold mechanism of the movable headrest disclosed in Patent Document 3 further comprises a fan-shaped latch part which functions in association with the action of the headrest body, and a lever part which engages with the latch part. More specifically, the position hold mechanism of Patent Document 3 is configured in such a way that as the position of the headrest body changes, the latch part rotates and the headrest body changes its position to the emergency position, so that the latch part engages with the lever part to hold the headrest body in the emergency position. However, this position hold mechanism suffers upsizing of the fan-shaped latch part, the lever part, etc., which leads to upsizing of the entire headrest and an increase in the weight.
The movable headrest of Patent Document 3 is designed in such a way that, so as to return the headrest body, shifted to the emergency position, to the normal position, the hold state of the position hold mechanism is released by disengaging the latch part from the lever part by an exclusive reset tool prepared separately. Furthermore, when returning the headrest body, a worker needs to return the headrest body to the normal position with one hand while disengaging the latch part from the lever part by means of the reset tool held by the other hand. Therefore, the work of returning the headrest body is very troublesome. In addition, because the latch part and the lever part are provided inside the headrest body, the worker cannot disengage both parts from each other without the reset tool in hand, disabling returning of the headrest body to the normal position.
As mentioned above, each of the conventional movable headrests incorporates the position changing mechanism, the position hold mechanism, the position return mechanism and so forth, so that the increased number of components leads to upsizing, weight increase and cost increase of the headrest. To avoid upsizing of the conventional movable headrests, various headrests have been proposed in which typically, the headrest constituting members are divided into front and rear parts. However, the dividable type headrest has a parting line formed on its outer design surface, and is inferior from the design point of view. Further, the dividable type headrest may suffer a foreign object entering the inside from the boundary portion of the divided headrest constituting members, interfering with the operation of each mechanism. Therefore, the dividable type headrest needs an additional member, such as a cover, to prevent penetration of foreign objects, leading to a further cost increase.